Carbon stars at high Galactic latitude

Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R^(1/4) density profile for the Galactic halo. This density profile can be traced to ≈ 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data

On the application of radio frequency voltages to ion traps via helical resonators

Ions confined using a Paul trap require a stable, high voltage and low noise radio frequency (RF) potential. We present a guide for the design and construction of a helical coil resonator for a desired frequency that maximises the quality factor for a set of experimental constraints. We provide an in-depth analysis of the system formed from a shielded helical coil and an ion trap by treating the system as a lumped element model. This allows us to predict the resonant frequency and quality factor in terms of the physical parameters of the resonator and the properties of the ion trap. We also compare theoretical predictions with experimental data for different resonators, and predict the voltage applied to the ion trap as a function of the Q-factor, input power and the properties of the resonant circuit

Carbon stars at high Galactic latitude

Photometry and kinematics are presented for a sample of objective prism selected carbon stars towards the north and south Galactic poles. Distances are determined by fitting the infrared colors to a giant branch. If these stars are like the carbon stars seen in dwarf spheroidal galaxies, the median distance of the sample is 28 kpc. If they are more like the carbon stars found recently in the Galactic bulge, they may be only half as distant. The surface density of carbon stars as a function of distance is remarkably consistent with an R^(1/4) density profile for the Galactic halo. This density profile can be traced to ≈ 15 scale radii and fills a volume similar to that occupied by globular clusters. The data yield an effective radius of either 7.0 or 3.5 kpc depending on choice of distance scale. The velocity dispersion of the sample is 96 + 12 km/s. A kinematic model in which vertical velocity dispersion is independent of height above the Galactic plane seems in best accord with the data

Comprehensive analysis of the chromatin landscape in Drosophila melanogaster.

Chromatin is composed of DNA and a variety of modified histones and non-histone proteins, which have an impact on cell differentiation, gene regulation and other key cellular processes. Here we present a genome-wide chromatin landscape for Drosophila melanogaster based on eighteen histone modifications, summarized by nine prevalent combinatorial patterns. Integrative analysis with other data (non-histone chromatin proteins, DNase I hypersensitivity, GRO-Seq reads produced by engaged polymerase, short/long RNA products) reveals discrete characteristics of chromosomes, genes, regulatory elements and other functional domains. We find that active genes display distinct chromatin signatures that are correlated with disparate gene lengths, exon patterns, regulatory functions and genomic contexts. We also demonstrate a diversity of signatures among Polycomb targets that include a subset with paused polymerase. This systematic profiling and integrative analysis of chromatin signatures provides insights into how genomic elements are regulated, and will serve as a resource for future experimental investigations of genome structure and function

Structural and functional characterizations of mung bean mitochondrial nucleoids

Mitochondrial nucleoids isolated from mung bean seedlings exhibited a chromatin-like structure associated with a membrane component. A similar structure, which underwent discrete changes during cotyledon development, was identified in situ. Isolated nucleoids consisted of essentially the same phospholipids, including cardiolipin, as whole mitochondria and proteins of inner- and outer-mitochondrial-membrane origin. Actin was consistently found with mitochondrial nucleoids prepared with different detergent concentrations. Formaldehyde cross-linking of cytochalasin B- and proteinase K-treated mitochondria further revealed that actin was associated with DNA in nucleoids. Mitochondrial nucleoids were self-sufficient in directing DNA synthesis in vitro in a pattern mimicking mtDNA synthesis in isolated mitochondria. In pulse-field gel electrophoresis, newly synthesized mtDNA separated into two major components, well-bound and fast-moving forms. Nucleoids DNA synthesis was resistant to aphidicolin but sensitive to N-ethylmaleimide, which indicates that a γ-type DNA polymerase was responsible for this activity. Mitochondrial nucleoids were capable of self-directed RNA transcription in a non-random fashion in vitro. Consistent with and complementary to results from fungi and human cells done mostly in situ, our present work helps to establish the important paradigm that mitochondrial nucleoids in eukaryotes are more than mere mtDNA compaction and segregation entities but are centers of mtDNA maintenance and expression

Nucleosynthesis in Electron Capture Supernovae of AGB Stars

We examine nucleosynthesis in the electron capture supernovae of progenitor AGB stars with an O-Ne-Mg core (with the initial stellar mass of 8.8 M_\odot). Thermodynamic trajectories for the first 810 ms after core bounce are taken from a recent state-of-the-art hydrodynamic simulation. The presented nucleosynthesis results are characterized by a number of distinct features that are not shared with those of other supernovae from the collapse of stars with iron core (with initial stellar masses of more than 10 M_\odot). First is the small amount of 56Ni (= 0.002-0.004 M_\odot) in the ejecta, which can be an explanation for observed properties of faint supernovae such as SNe 2008S and 1997D. In addition, the large Ni/Fe ratio is in reasonable agreement with the spectroscopic result of the Crab nebula (the relic of SN 1054). Second is the large production of 64Zn, 70Ge, light p-nuclei (74Se, 78Kr, 84Sr, and 92Mo), and in particular, 90Zr, which originates from the low Y_e (= 0.46-0.49, the number of electrons per nucleon) ejecta. We find, however, that only a 1-2% increase of the minimum Y_e moderates the overproduction of 90Zr. In contrast, the production of 64Zn is fairly robust against a small variation of Y_e. This provides the upper limit of the occurrence of this type of events to be about 30% of all core-collapse supernovae.Comment: 13 pages, 14 figures, accepted for publication in Ap

Preferential Re-Replication of Drosophila Heterochromatin in the Absence of Geminin

To ensure genomic integrity, the genome must be duplicated exactly once per cell cycle. Disruption of replication licensing mechanisms may lead to re-replication and genomic instability. Cdt1, also known as Double-parked (Dup) in Drosophila, is a key regulator of the assembly of the pre-replicative complex (pre-RC) and its activity is strictly limited to G1 by multiple mechanisms including Cul4-Ddb1 mediated proteolysis and inhibition by geminin. We assayed the genomic consequences of disregulating the replication licensing mechanisms by RNAi depletion of geminin. We found that not all origins of replication were sensitive to geminin depletion and that heterochromatic sequences were preferentially re-replicated in the absence of licensing mechanisms. The preferential re-activation of heterochromatic origins of replication was unexpected because these are typically the last sequences to be duplicated in a normal cell cycle. We found that the re-replication of heterochromatin was regulated not at the level of pre-RC activation, but rather by the formation of the pre-RC. Unlike the global assembly of the pre-RC that occurs throughout the genome in G1, in the absence of geminin, limited pre-RC assembly was restricted to the heterochromatin by elevated cyclin A-CDK activity. These results suggest that there are chromatin and cell cycle specific controls that regulate the re-assembly of the pre-RC outside of G1

DNA replication timing is deterministic at the level of chromosomal domains but stochastic at the level of replicons in Xenopus egg extracts

Replication origins in Xenopus egg extracts are located at apparently random sequences but are activated in clusters that fire at different times during S phase under the control of ATR/ATM kinases. We investigated whether chromosomal domains and single sequences replicate at distinct times during S phase in egg extracts. Replication foci were found to progressively appear during early S phase and foci labelled early in one S phase colocalized with those labelled early in the next S phase. However, the distribution of these two early labels did not coincide between single origins or origin clusters on single DNA fibres. The 4 Mb Xenopus rDNA repeat domain was found to replicate later than the rest of the genome and to have a more nuclease-resistant chromatin structure. Replication initiated more frequently in the transcription unit than in the intergenic spacer. These results suggest for the first time that in this embryonic system, where transcription does not occur, replication timing is deterministic at the scale of large chromatin domains (1–5 Mb) but stochastic at the scale of replicons (10 kb) and replicon clusters (50–100 kb)

Expression in Aneuploid Drosophila S2 Cells

Analysis of the relationship between gene copy number and gene expression in aneuploid male Drosophila cells reveals a global compensation mechanism in addition to X chromosome-specific dosage compensation

Global Profiling of DNA Replication Timing and Efficiency Reveals that Efficient Replication/Firing Occurs Late during S-Phase in S. pombe

10.1371/journal.pone.0000722PLoS ONE2